1. Technical Field
The present invention pertains broadly to the field of heat exchangers, and specifically to wound, spine fin coil type heat exchangers having multi-circuits.
2. Prior Art
Helically wound fin tube coils are frequently used for outdoor heat exchangers in air conditioning units including cooling-only units and heat pumps. The wound coils provide an adequate heat exchange surface for the outdoor heat exchanger in an acceptable size, and can be relatively inexpensively manufactured, particularly for residential size units. The outdoor heat exchanger of the air conditioner frequently includes a plurality of circuits, and the coil may be wound in generally rectangular or annular shapes. The coil is disposed on a frame or base, with a guard disposed therearound and a cover or grill disposed on the top thereof for protection, the guard, cover and base essentially defining the perimeter of the outdoor unit. Arranged within the space defined by the coil of conventional units are the compressor, outdoor fan, inlet and outlet manifolds, expansion valves, check valves, filters driers and, in a heat pump, a reversing valve, with appropriate interconnecting refrigerant lines therebetween. A compact outdoor unit is thus provided, requiring only hookup to the indoor heat exchanger and an electric power source.
Typical manufacturing methods for such coils include winding the entire coil, either vertically or horizontally, from a continuous length of fin tubing, and thereafter determining in which wraps inlets and outlets for adjacent circuits should be made. Two cuts are made, and a section of tubing is removed from each wrap which is determined to be a location for circuit ends. Transition tubes leading to the manifolds are connected to the cut ends of the heat exchange tubing. The sections of fin tubing are removed to allow adequate space for the manifolds and for the transition tubes to be disposed at a downward angle from the circuit ends. Since the fin tube of the coil is often made of aluminum while the refrigerant lines are copper, the downward slope of the transition tubes is necessary to permit water to flow away from the aluminum to prevent corrosion from a galvanic reaction. The transition tubes are pre-tinned copper tubes having tapered ends which are inserted into the ends of the circuits and soldered in place.
In rectangularly shaped coils the spacing for manifolds usually has been achieved by removing a section of heat exchange tube which extends around a corner of a wrap, and the manifolds are provided one along each of two adjacent coil sides. The tube section removed is wasted in both economic and heat exchange efficiency terms. When a coil contains relatively long circuits few in number the amount of waste is insignificant. More recently however, in striving for increased efficiency for heat pumps or cooling-only air conditioners, it has been found desirable to increase the heat exchange capacity of the outdoor coil. This can be achieved by increasing the number of circuits in the outdoor coil. The waste resulting from removing a section of each coil wrap in which a break is made for circuit ends becomes significant, amounting to as much as five percent (5%) of the total material in the coil. The need for adequate room for manifolds remains, and the actual requirement is increased as the number of circuits are increased. It becomes more difficult to arrange the manifolds, refrigerant lines and transition tubes to ensure that no copper tubes are located above aluminum tubes, and that all aluminum to copper connections are disposed angularly downward away from the aluminum tubes. Thus, manufacturing and assembly become more costly and more difficult, and heat exchange capacity is more significantly influenced in heat exchangers having increased numbers of circuits.